Bob Owns a Watch Repair Shop $c ( x ) = 2 x ^ { 2 } - 156 x + 88$

Multiple Choice

Bob owns a watch repair shop. He has found that the cost of operating his shop is given by $c ( x ) = 2 x ^ { 2 } - 156 x + 88$ , where c is cost and x is the number of watches repaired. How many watches must he repair to have the lowest cost?

A) 44 watches
B) 88 watches
C) 20 watches
D) 39 watches